Synthesis of ionically conductive compositions of matter using amine solvents

ABSTRACT

A process for the preparation of a solid ionically conductive composition of matter of either the formula: 1. MAg4I5 in which M is Rb, K, NH4, Cs, or combinations thereof, Cs being present only as a minor constituent of M; or 2. QAgnIn 1, where n has a value from 3 to 39 inclusive and Q is an organic ammonium cation having an ionic volume between 30 and 85 cubic angstroms, comprising reacting approximately stoichiometric quantities, corresponding to the ionically conductive compositions formed, of AgI and either MI or QI in a liquid reaction medium that is a water-containing selected amine solvent, and separating the synthesize ionically conductive composition from the reaction medium.

United States Patent [191 Topol et al.

[ 1 March 6, 1973 SYNTHESIS OF IONICALLY CONDUCTIVE COMPOSITIONS OF MATTER USING AMINE SOLVENTS [75] Inventors: Leo E. Topol; Herman Mandel, both of Canoga Park, Calif.

[73] Assignee: North American Rockwell Corporation, El Segundo, Calif.

[22] Filed: Dec. 8, 1970 [21] App]. No.: 96,226

[52] US. Cl ..252/518, 423/463 [51] Int. Cl. ..I-I01b 1/02 [58] Field of Search ..252/518; 23/87, 89, 367

[56] References Cited UNITED STATES PATENTS 3,519,404 7/l970 Argue et al ..252/518 2,994,975 7/1960 Folberth 2,944,975 7/1960 Folberth ..23/204 OTHER PUBLICATIONS Primary Examiner--George F. Lesmes Assistant Examiner-J. P. Brammer fAttorney-L. Lee Humphries, Thomas S. MacDonald and Henry Kolin [57] ABSTRACT i A process for the preparation of a solid ionically conductive composition of matter of either the formula: 1

i 1. MAgJ, in which M is Rb, K, NH Cs, or combinations thereof, Cs being present only as a minor constituent of M; or

i 2. QAg,,L, where n has a value from 3 to 39 inclusive and Q is an organic ammonium cation having an ionic volume between 30 and 85 cubic angstroms, comprising reacting approximately stoichiometric iquantities, corresponding to the ionically conductive compositions formed, of Agl and either Ml or QI in a liquid reaction medium that is a water-containing selected amine solvent, and separating the synthesize ionically conductive composition from the reaction medium.

10 Claims, No Drawings SYNTHESIS OF IONICALLY CONDUCTIVE COMPOSITIONS OF MATTER USING AMINE SOLVENTS BACKGROUND OF THE INVENTION This invention relates to a process for the preparation of ionically conductive compositions of matter having unusually high ionic conductivity. It particularly relates to a process for the preparation of compounds having the formula MAgJ in which M is Rb, NI-l K, Cs, or a combination of these, Cs being present only as a minor constituent of M; and 2 QAg,,l,, where n has a value from 3 to 39 inclusive and O is an organic ammonium cation having an ionic volume between 30 and 85 cubic angstroms. Such compositions are particularly useful as electrolytes in solid state electric cells. Electric cells containing these electrolyte materials are described in U. S. Pat. Nos. 3,443,997 and 3,476,606, respectively.

Compositions of the foregoing type, MAg l and QAg L have recently been shown to have high ionic conductivity in the solid state over a wide range of temperatures. The known methods of preparing these compositions involve mixing appropriate amounts of the solid reactants Ml and Agl or 01 and Agl in the desired molar ratios,and either heating the mixture until molten, followed by a holding period at a lower temperature to form the desired compound (meltqnneal technique), or reacting the solid reactants in a timeconsuming solid-state reaction at an annealing temperature of 200C or higher to form the compound. In an alternative method'of preparation of MAgJ the constituents are dissolved in acetone and precipitated by evaporation. However, this method results ina mixture of the desired compound and another compound, generally of high resistivity, rather than the pure ionically conductive composition. For preparing the organic silver ammonium iodide compositions, QAg.l,, a paste preparation technique has also been used in which a slurry or paste is preparedof the silver iodide and the organic ammonium iodide, followed by a multiple annealing technique. Synthesis in an aqueous medium in which the silver iodide and organic ammonium iodide reactants and the formed product exhibit only a limited solubility has also, been suggested as feasible.

The present invention provides a simple and convenient method for thepreparation of solid ionically conductive materials from selected organic amine solutions. The process of this invention is advantageous compared with the methods known to the prior art in that it is more easily adapted to large-scale production, provides for control or variation of the composition of the materials formed, and may be used to produce large crystals or thin films of the desired compound. The present process does not require the use of a high temperature, and the synthesized compositions may be easily recovered from the reaction medium.

The compositions prepared by the process of this invention have a high ionic conductivity and may be used in a variety of electrochemical devices. The process is of particular utility for preparing compositions for use in thin-film and single-crystal devices.

SUMMARY OF THE INVENTION The solid ionically conductive compositions which may be prepared by the process of this invention have either the general formula:

l. MAgJ in which M is Rb, K, NH Cs, or combinations thereof, Cs being present only as a minor constituent of M; or

2. QAg,,l,, where n has avalue from 3 to 39 inclusive and Q is an organic ammonium cation having an ionic volume between 30 and 85 cubic angstroms.

According to the process of this invention, Agl and a compound MI or Ql (M and Q as above defined) are reacted in approximately stoichiometric amounts, corresponding to the ratios of the compositions formed, in a selected liquid reaction medium which is a water-containing amine solution.

The organic amine serves to solubilize the silver iodide, with which it forms a soluble complex; the water present serves to solubilize the MI or QI compound. While both the Agl and MI or 01 may be added directly to the amine solution and containing a small amount of water, in the preferred aspects of practicing the invention the Agl is separately dissolved in a small amount of the organic amine, and M1 or 01 is separately dissolved in a minimum quantity of water sufficient to solubilize it. Then one liquid solution is added to the other. Generally the final amine solution will contain from 1 to 3 volume percent of water.

Suitable organic amines are those which readily dissolve or solubilize the silver iodide, are liquid at the reaction temperature and miscible with at least small amounts of water, and are volatilized below the decomposition temperature of the ionically conductive composition. Thus utilizable amines are generally selected from those having a boiling range between and 200C, preferably between 50 and 150C. Because amines readily form a complex with silver salts, thereby 5 solubilizing them, the selection of the organic amine to be utilized in the practice of this invention is not considered critical and may be readily determined within the requirements above set forth. Many commercially available amines are known and are utilizable in the practice of the present invention. They are conveniently classified as alkylamines, ethylene amines, alkanolamines, and arylamines, and include primary, secondary, and tertiary amines. Generally those liquid amines of low molecular weight, e.g., between 50 and 100, which are readily commercially available as inexpensive solvents are preferred. Illustrative of suitable alkylamines are diethylamine, triethylamine, npropylamine, di-n-propylamine, di-isopropylamine, nbutylamine, n-dibutylamine, isobutylamine, diisobutylamine, sec-butylamine, n-amylamine, secamylamine, sec-hexylamine, Z-ethylbutylamine, n-heptylamine, and 2-ethylhexylamine. Suitable alkylene include preferred amine solvents are pyridine, allylamine, diethylamine, and ethylenediamine. After reaction, the synthesized compositions are recovered from the reaction medium by precipitation, either by adding an additional component to reduce the solubility of the composition or by evaporating the solvent away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS ln the practice of the process of the present invention in its preferred aspects, the appropriate amount of silver iodide is dissolved in the selected liquid organic amine, which has been warmed to at least room temperature, preferably between 50 and 100C, to form a concentrated solution. The appropriate amount of the second iodide, Ml or QI or combination of iodides, is then added, preferably as anaqueous solution in a minimal amount of water. The amount of water utilized is not considered critical, but no advantages are obtained by using excess amounts of water and such use is disadvantageous because of the requirements for the subsequent removal of the solvents to recover the formed compound. Thus, while the water present in the amine solution may be as high as volume percent or greater, generally it will be present in an amount not greater than between 1 and 3 volume percent Because of the subsequent need for separating the ionically conductive composition from the reaction medium, it is preferred that both the initial amine solution and the initial aqueous solution be prepared as concentrated solutions so as to minimize the quantities of solvent required to be volatilized. The relative stoichiometric amount of the second iodide to be added to the silver iodide is determined by the composition of the ionically conductive compound to be prepared. For example, to form a composition RbAg I,, the components are used in a ratio of 4AgIzRbl.

In preparing the alkali metal silver iodides, the

. secbnd iodide may be rubidium iodide, potassium iodide, ammo'nium iodide, cesium iodide orcombinations thereof. Cesium iodide where used constitutes less than' 50 percent by weight of the second iodide and is present only in combination with one or more of the other alkali metal iodides.

To prepare the organically substituted ammonium silver iodides, the organic ammonium iodide components and the molar ratiosused are essentially as described in US. Pat. No. 3,476,606, particularly as set forth in Column 3 thereof. Thus n moles of Ag! will be reacted with each mole of Q] to give the organic ammonium silver iodide compound having the formula QAg l t, where n has any value between 3 and 39. Preferably, 4 to 9 molar portions of silver iodide are reacted with each molar portion of 01. For example, to prepare a preferred compound, 6% moles of'Agl are reacted with 1 mole of NRJ, where R is preferably a lower alkyl group such as methyl ethyl, propyl, or butyl. While pyridine, allylamine, diethylamine, and ethylenediamine have been found to be especially useful amine solvents, their use is not critical'and other amines may be used in the practice of this invention as above set forth.

The process may be carried out at any suitable temperature which is belowthe boiling point of the liquid reaction medium, for example, from slightly above 7 ness. The solid which remains is the ionically conductive material. This is dried by heating it at a temperature of about 50150C for 0.5 to 5 hours.

In another method, after a single-phase reaction medium is obtained, the ionically conductive composition is separated as a solid by extraction from the reaction medium with an alcohol at room temperature or preferably warmed, e.g., 40-60C. To the reaction medium containing the synthesized ionically conductive composition, an approximately equal volume of warm lower alkyl alcohol is added. The mixture is stirred briefly and allowed to separate into layers. The upper alcohol layer contains a white solid; this alcohol layer is separated from the reaction medium, for example, by decanting and filtering the alcohol 'while warm or by other suitable methods. After removal of the alcohol, the residue, which is the solid ionically conductive composition, is dried, for example, by heating at 50l 50C for about 0.5 to 5 hours. Ethanol and isopropyl alcohol are especially useful for extracting the ionically conductive composition in this second method. In using this method, care must be taken to avoid the use of excess amounts of alcohol sinzfce this may result in precipitation of small amounts of Ag] from the reaction medium, thereby contaminating{ the ionically conductive composition.

With either of the methods described above, a purer product may be obtained by washing the precipitate with a dry lower alkyl alcohol; or fractional crystallization may be employed, using the amine solvent and a lower alkyl alcohol. In this manner, any alcohol-soluble compounds that may have coprecipitated with the ionically conductive composition, or any amine solvent still remaining with the composition, can more effectively be removed.

The present process is especially useful for preparing ionically conductive compositions of matter for use in thin-film and single-crystal electrochemical devices. By suitable control of the conditions of precipitation and evaporation, thin films or large single crystals of the compositions may be produced in a relatively simple manner, since removal of the solvent by evaporation leaves the compound behind.

The following examples serve to illustrate the invention, but are in no way considered limiting thereto:

EXAMPLE 1 6.5 g. Ag] was dissolved in 30 ml. pyridine at 60C. To this solution was added 1.5 g. Rbl dissolved in 0.8 ml. water. After obtaining a single-phase solution, the resulting solution was evaporated to dryness on a hot plate, and .the residue was then dried in an oven at C for-three-fourths hour. The material formed was essentially RbAgJ as shown by X-ray and conductivity measurements.

EXAMPLE 2 The process of Example I was followed, except that after obtaining a single-phase solution, 30 ml. isopropyl alcohol which had been warmed to 50C was added to the solution and stirred briefly. After standing for l to 2 minutes, the mixture separated into two layers, with the upper alcohol layer containing a white solid. The upper layer was separated, decanted, and filtered. A white residue was recovered, which was dried at 110C for an hour. This residue was found to be essentially RbAg l by X-ray and conductivity tests.

EXAMPLE 3 2.85 g. Agl was dissolved in 30 ml. pyridine. To this solution was added 0.5 g. KI dissolved in 0.5 ml. water. The solution was stirred and then evaporated to dryness in an oven at a temperature of about 120C. The material formed was essentially KAgJ; as shown by X- ray and conductivity measurement.

EXAMPLE 4 N(C H l.6%AgI was prepared following the general procedure shown in Example 3. 5.59 g. Agl 1.0 g. N(C H l in 25 ml. pyridine plus 0.5 ml water were used. A clear solution was obtained. The solution was stirred and then evaporated to. dryness in an oven at a temperature of about 120C. The material formed was essentially N(C,H I.b%AgI as shown by X-ray and conductivity measurements.

EXAMPLE 5 RbAg l was prepared from an allylamine solution following the general procedure shown in Example 3. 1.62 g. Agl was dissolved in ml. allylamine, and this solution was reacted with 0.37 g. Rbl in 1 ml. water. The solution was stirred and then evaporated to dryness in an oven at a temperature of about 120C. The material formed was essentially RbAg I as shown by X-ray and conductivity measurements.

EXAMPLE 6 EXAMPLE 7 To 25 ml. diethylamine was added 1.62 g. Agl and 1 ml. water containing 0.37 g. Rbl dissolved therein. The resultant solution was evaporated on a hot plate, and then dried for 2 hours in a 140C over. The material formed was essentially RbAg l as shown by x-ray and conductivity measurements.

EXAMPLE 8 1.62 g. Agl was dissolved in ml. ethylenediamine. To this was added 0.37 g. Rbl in 1 ml. water. The single-phase solution obtained was evaporated down on a hot plate, and the obtained residue was dried in a 150C oven for 2 hours. The material formed was essentially RbAgJ, as shown by x-ray and conductivity measurements.

Compounds made according to the process of this invention are prepared combining stoichiometric proportions corresponding to 4AgIzMl or nAglzQI, e.g., RbAgJ, or 6%AgI:N(C H l. However, small amounts of the starting compounds or of adventitious impurities which may be present will not unduly decrease the ionic conductivity values. Further, certain inorganic compounds such as silica as well as organic polymers and other additives may be inclined with the pure compounds for purposes of moisture absorption, stability, etc.

It will of course be realized that various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principle, preferred construction, and mode of operation of the invention have been explained and what is now considered to represent its best embodiment has been illustrated and described, it should be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. A process for preparing a solid ionically conductive composition of matter of the general formula: (1) MAgJ, where M is Rb, K, NH Cs, or combinations thereof, Cs being present only in combination as a minor constituent of M; or (2) QAg,,I, where n has a value from 3 to 39 inclusive and Q is an organic ammonium cation having an ionic volume between 30 and cubic angstroms; which process comprises the steps of (a) reacting silver iodide with a second iodide compound selected from MI and QI in a single-phase liquid reaction medium which is a water-containing amine solution, the second iodide compound and silver iodide being present in the reaction medium is about stoichiometric amounts, corresponding to the ionically conductive composition prepared, and (b) separating the so-prepared solid ionically conductive composition of matter from the reaction medium.

2. The process according to claim 1 wherein the second iodide compound is added in the form of an aqueous solution to the amine which contains the Agl.

3. The process according to claim 1 wherein the single-phase reaction medium contains between 1 and 3 volume percent water.

4. The process according to claim 1 wherein the temperature of the reaction medium is between about 50 and C.

5. The process according to claim 1 wherein the amine is selected from the group consisting of pyridine, allylamine, diethylamine, and ethylenediamine.

6. The process according to claim 1 wherein step (b)- comprises evaporating the reaction medium to dryness and drying the remaining solid ionically conductive compound thereby separating the ionically conductive composition from the reaction medium.

7. The process according to claim 1 wherein step (b) comprises adding a lower alkyl alcohol to the reaction medium containing the ionically conductive composition, stirring, separating the reaction medium into an upper alcohol layer containing the ionically conductive composition and a lower amine layer, and recovering is RbAg l I 10. The process according to claim 1 wherein an organic ammonium silver iodide composition is prepared by reacting from 4 to 9 moles of Ag! with each mole of NR where R represents at least one lower alkyl group selected from methyl, ethyl, propyl, and butyl.

STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,719,611 Dated March Q, 1973 Inventofls) Q Topol et a1 It is certified that error appears in the aboveddentified patent and that said Letters Patent are hereby corrected as shown below:

" Cover page under "References Cited" delete "2,944,975 .1 7/1960 Folberth 23/2o w (second instance); Cover page under "Other Publications" should read --Jacobson: Encyclopedia of Chemical Reactions, Vol. VI, 1956, p'. 162.--; Cover page under "Abstract" third line from bottom "synthesize" should read ---synthesized I Column 1, line 10 after "formula" insert --(1)--' Column 1, line 12 "2 Q,Ag' l[ should read --(2) QAg I Column 2, line 60 "Z-amino-butanol" should read --2-amino-1- butanol--.

Column 5 line 26 "N(C H I.b /2AgI" should read --N(C H s, I.6 /2AgI--;

Column 5, line 59 "over." should read --oven.--. M Column 6, line 12 "inclined" should read --included--;

Column 6, line 39 "is" should read --in--.

v Signed and sealed this 21st day of I'Iay 1971.14

(SEAL) Attest:

EDWARD I I.FLETUIMR,JR. C I IAHSHALL DANN [attesting Officer Commissioner of Patents 

1. A process for preparing a solid ionically conductive composition of matter of the general formula: (1) MAg4I5 where M is Rb, K, NH4, Cs, or combinations thereof, Cs being present only in combination as a minor constituent of M; or (2) QAgnIn 1 where n has a value from 3 to 39 inclusive and Q is an organic ammonium cation having an ionic volume between 30 and 85 cubic angstroms; which process comprises the steps of (a) reacting silver iodide with a second iodide compound selected from MI and QI in a single-phase liquid reaction medium which is a water-containing amine solution, the second iodide compound and silver iodide being present in the reaction medium is about stoichiometric amounts, corresponding to the ionically conductive composition prepared, and (b) separating the so-prepared solid ionically conductive composition of matter from the reaction medium.
 1. MAG415 IN WHICH M IS RB, K, NH4, CS, OR COMBINATIONS THEREOF, CS BEING PRESENT ONLY AS A MINOR CONSTITUENT OF M; OR
 2. QAGNIN+1, WHERE N HAS A VALUE FROM 3 TO 39 INCLUSIVE AND Q IS AN ORGANIC AMMONIUM CATION HAVING AN IONIC VOLUME BETWEEN 30 AND 85 CUBIC ANGSTROMS, COMPRISING REACTING APPROXIMATELY STOICHIOMETRIC QUANTITIES, CORRESPONDING TO THE IONICALLY CONDUCTIVE COMPOSITIONS FORMED, OF AGI AND EITHER MI OR QI IN A LIQUID REACTION MEDIUM THAT IS A WATER-CONTAIN ING SELECTED AMINE SOLVENT, AND SEPARATING THE SYNTHESIZE IONICALLY CONDUCTIVE COMPOSITION FROM THE REACTION MEDIUM.
 2. The process according to claim 1 wherein the second iodide compound is added in the form of an aqueous solution to the amine which contains the AgI.
 3. The process according to claim 1 wherein the single-phase reaction medium contains between 1 and 3 volume percent water.
 4. The process according to claim 1 wherein the temperature of the reaction medium is between about 50 and 150* C.
 5. The process according to claim 1 wherein the amine is selected from the group consisting of pyridine, allylamine, diethylamine, and ethylenediamine.
 6. The process according to claim 1 wherein step (b) comprises evaporating the reaction medium to dryness and drying the remaining solid ionically conductive compound thereby separating the ionically conductive composition from the reaction medium.
 7. The process according to claim 1 wherein step (b) comprises adding a lower alkyl alcohol to the reaction medium containing the ionically conductive composition, stirring, separating the reaction medium into an upper alcohol layer containing the ionically conductive composition and a lower amine layer, and recovering the ionically conductive composition from the alcohol layer.
 8. The process according to claim 7 wherein the lower alkyl alcohol is selected from ethanol and isopropyl alcohol.
 9. The process according to claim 1 wherein M is Rb and the formed solid ionically conductive composition is RbAg4I5. 